Many different things could have happened when Jimmy recognized Bob in the short story "After Twenty Years."

First, Jimmy would have had to arrest Bob immediately. Jimmy knew that Bob had an arrest warrant out for his arrest and, as an officer of the law, would have been forced to arrest Bob. Given that Jimmy could not bring himself to do this, he arranged for another office to arrest Bob.

Second, Bob may have ran. After recognizing Jimmy as an officer of the law, Bob may have figured that his past had caught up with him and that he had no choice but to run.

Lastly, Jimmy could have decided not to identify Bob as the criminal. Jimmy could have let Bob go based upon their past friendship. Bob could have gotten off free and clear had Jimmy not given him up.

In the end, Jimmy's honor to his friendship and his position as an officer of the law created quite a conflict for Jimmy. Knowing that he was betraying Bob, Jimmy felt he had to explain to Bob why he was getting arrested. Jimmy wrote the following note to Bob explaining:

"Bob: I was at the appointed place on time. When you struck the match to light your cigar I saw it was the face of the man wanted in Chicago. Somehow I couldn't do it myself, so I went around and got a plain clothes man to do the job. JIMMY."

This is an interesting question. O. Henry always wrote heavily plotted stories. He may have started with the idea of having Jimmy Wells reveal himself as the uniformed cop who was talking to "Silky" Bob in the doorway. But having Jimmy arrest Bob would have led to endless complications. Bob, of course, would have tried to talk Bob out of arresting him and then, if he was unsuccessful in that attempt, he would probably have gone on to berate his old friend for such heartlessness. After all, Bob would say, he had come all the way from Chicago, a distance of around a thousand miles, just to keep an engagement they had made twenty years ago. How could Jimmy do such a thing? The ending would have been tremendously complicated--yet it would have been even more complicated if O. Henry had decided to have Jimmy let Bob go free. Then it would look as if Jimmy was violating his oath to uphold the law and that he was becoming an accessory to whatever crime or crimes Bob was wanted for. In either case, O. Henry would not be able to close his story with one of the surprise endings for which he is famous. So the author took a round-about route and had Bob arrested by a plain clothes officer who was a complete stranger. Evidently O. Henry decided that he just did not want to have Jimmy make the arrest in person even though we realize that Bob would never have been arrested if it hadn't been for Jimmy. The plot is still very complicated, but at least the ending is simple and comes as a big surprise.